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High temperature decomposition and age hardening of single-phase wurtzite Ti1−xAlxN thin films grown by cathodic arc deposition
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering. Seco Tools AB, Sweden.ORCID iD: 0000-0002-1443-8359
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0002-6033-1130
Sandvik Coromant AB, Sweden.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.ORCID iD: 0000-0001-6373-5109
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2024 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 8, no 1, article id 013602Article in journal (Refereed) Published
Abstract [en]

Wurtzite TmAlN (T-m = transition metal) themselves are of interest as semiconductors with tunable band gap, insulating motifs to superconductors, and piezoelectric crystals. Characterization of wurtzite TmAlN is challenging because of the difficulty to synthesize them as single-phase solid solution and such thermodynamic, elastic properties, and high temperature behavior of wurtzite Ti1-xAlxN is unknown. Here, we investigated the high temperature decomposition behavior of wurtzite Ti1-xAlxN films using experimental methods combined with first-principles calculations. We have developed a method to grow single-phase metastable wurtzite Ti1-xAlxN (x = 0.65, 0.75, 085, and 0.95) solid-solution films by cathodic arc deposition using low duty-cycle pulsed substrate-bias voltage. We report the full elasticity tensor for wurtzite Ti1-xAlxN as a function of Al content and predict a phase diagram including a miscibility gap and spinodals for both cubic and wurtzite Ti1-xAlxN. Complementary high-resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950 degrees C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semicoherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1-2 GPa.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC , 2024. Vol. 8, no 1, article id 013602
National Category
Materials Chemistry
Identifiers
URN: urn:nbn:se:liu:diva-200673DOI: 10.1103/PhysRevMaterials.8.013602ISI: 001147553300004OAI: oai:DiVA.org:liu-200673DiVA, id: diva2:1835444
Note

Funding Agencies|Swedish National Infras-tructure for Computing (SNIC) - Swedish Research Council [VR-2015-04630]; Swedish National Infrastructure for Computing (SNIC); National Academic Infrastructure for Supercomputing in Sweden (NAISS); Swedish Research Council [VR-2015-04630]; VINNOVA (FunMat-II project) [2022-03071]; Swedish Research Council (VR) [2017-03813, 2017-06701, 2021-04426, 2021-00357, 2019-00191]; Swedish government strategic research area [AFM-SFO MatLiU (2009-00971)]; Knut and Alice Wallenberg Foundation [KAW-2018.0194]

Available from: 2024-02-06 Created: 2024-02-06 Last updated: 2024-04-02
In thesis
1. Combining ab‐initio and machine learning techniques for theoretical simulations of hard nitrides at extreme conditions
Open this publication in new window or tab >>Combining ab‐initio and machine learning techniques for theoretical simulations of hard nitrides at extreme conditions
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis I focus on combining the high accuracy of first-principles calculations with modern machine learning methods to make large scale investigations of industrially relevant nitride systems reliable and computationally viable. I study the electronic, thermodynamic and mechanical properties of two families of compounds: Ti1−xAlxN alloys at the operational conditions of industrial cutting tools and ReNx systems at crushing pres-sures comparable to inner earth core conditions. Standard first-principles simulations of materials are usually carried out at zero temperature and pressure, and while many state-of-the-art approaches can take these effects into account, they are usually accompanied by a substantial increase in computational demand. In this thesis I therefore explore the possiblities of studying materials at extreme conditions using machine learning methods with extraordinary efficiency without loss of calculational accuracy. 

Ti1−xAlxN alloy coatings exhibit exceptional properties due to their inherent ability to spinodally decompose at elevated temperature, leading to age-hardening. Since the cubic B1 phase of Ti1−xAlxN is well-studied, available high-accuracy first-principles data served as both a benchmark and data set on which to train a machine learning interatomic potential. Using the reliable moment tensor potentials, an investigation of the accuracy and efficiency of this approach was carried out in a machine learning study. Building upon the success of this technique, implementation of a learning-on-the-fly (active learning) methodology into a workflow to determine accurate material properties with minimal prior knowledge showed great promise, while maintaining a computational demand up to two orders of magnitude lower than comparable first-principles approaches. Investigations of properties of industrially lesser desired, but sometimes present hexagonal alloy phases of Ti1−xAlxN are also included in this thesis, since knowledge and understanding of all competing phases can help guide development toward improving cutting tool lifetime and performance. Furthermore, while w-Ti1−xAlxN may not be able to compete with its cubic counterpart in terms of hardness, it shows promise for other applications due to its electronic and elastic properties. 

Metastable ReNx phases are high energy materials due to their covalent N-N and Re-N bonds, leading to exceptional mechanical and electronic properties. Just like diamond, the hardest and arguably most famous metastable mate-rial naturally occurring on earth, they are stabilized by extreme pressures and high temperatures, but can be quenched to ambient conditions. Understanding the formation and existence of these non-equilibrium compounds may hold the key to unlocking a new generation of hard materials. In this thesis, all currently known phases of ReNx compounds have been investigated, encompassing both experimentally observed and theoretically suggested structures. Investigations of the convex hulls across a broad pressure range were carried out, coupled with calculations of phonons in the proposed crystals to determine both energetic and dynamical stability. Overall, the studies included in this thesis focused mainly on investigation of the ground state of ReN2 at higher pressure, where experimental results were deviating from earlier theoretical predictions. Additional research focused on specifically exploring properties and stability of novel ReN6 at synthesis conditions using the active learning workflow to train an interatomic potential. 

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2024. p. 87
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 2375
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:liu:diva-201992 (URN)10.3384/9789180755320 (DOI)9789180755313 (ISBN)9789180755320 (ISBN)
Public defence
2024-04-19, Planck, F-building, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2024-04-02 Created: 2024-04-02 Last updated: 2024-04-02Bibliographically approved

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